This invention relates to a process for finishing a 15.degree. to 180.degree. pipe bend which has been preformed on a pipe bending press, as well as to a machine for performing the process.
Processes for the production of pipe bends have been known in the art for a long time. Calculated lengths of pipe are cut off a straight pipe to provide blanks which are bent over a conventional knee or bending mandrel. By this operation the blank is deformed to a pipe bend, the pipe bending press delivering preformed 15.degree. to 180.degree. bends.
According to the nature and state of the material these preformed bends leave the pipe bending press at a temperature between 700.degree. and 900.degree. C. The diameter of the bends after they have been bent is no longer uniform and it is therefore necessary to correct this by sizing the preforms in a die. Horizontal dies are normally used for this sizing operation. After sizing it is necessary to cool the pipe bend before it is subjected to further operations.
As soon as the pipe bend is sufficiently cool it is taken to the trimming shop. Here the pipe bend is cut to a 90.degree. angle by a two-cut or three-cut saw. Naturally other angles can be cut if desired. However, this trimming operation is always performed within the upper tolerance range. Sometimes even this may be exceeded, in which case the pipe bend must be subjected to further finishing work to comply with design dimensions. However, cold sizing merely relates to the finishing of the ends, i.e. the ends of the pipe bend are reduced to within the admissible tolerance range. Should the end finishing operation affect the angle of the pipe bend, then the ends must be reground to the wanted angle, e.g. 90.degree. . Regrinding will also be necessary if the pipe bend had not been precisely clamped up to the saw blade which will then make an oblique cut. All this finishing work which is necessary to keep within the prescribed tolerance limits is mainly manual work. Recently tolerances for pipe or tube bends used in marine engineering have been further tightened with a consequential rise in the cost of production due to the extra finishing work, bearing in mind that normal tolerances are already difficult to observe.